Fig. 5. Effect of surface functionalization on metal ion sensing by N-MQDs. (A and C) Fluorescence emission spectra of N-MQDs in the presence of increasing concentrations of Fe³⁺ and Cu²⁺ ions. (B and D) Corresponding calibration curves based on normalized fluorescence quenching, demonstrating enhanced sensitivity and linear response enabled by amino functionalization. Adapted with permission from ref. 75. © 2022, the American Chemical Society.